Understanding Blood Tube Colours and What Each One Means
, by Andrew Odgers, 10 min reading time
Reference Guide
Understanding Blood Tube Colours and What Each One Means
Blood collection tube cap colours identify the additive inside and therefore the sample type the tube will produce and the tests it can support. The colour coding system is internationally recognised, though minor variations exist between manufacturers. This guide provides the complete reference for UK laboratory practice, covering every standard colour, its additive, the sample type produced, and the tests it is used for.
Colour reference
Blood tube colours and their additives
The following covers the standard cap colours used across UK laboratory practice. Minor variations exist between tube manufacturers; always confirm the additive on the tube label.
- Gold or yellow-grey (SST): serum separator tube. Contains a clot activator and inert gel. Blood clots and centrifugation separates gel-sealed serum. Used for most routine biochemistry (U&E, LFTs, TFTs, lipids, CRP, HbA1c, immunology). The most widely used tube in routine biochemistry practice.
- Red (plain): no additive. Blood clots naturally producing serum without gel. Used where gel may interfere with the assay, including some drug level monitoring, blood bank crossmatch, and specialist immunology. Less common than SST in routine UK practice.
- Purple or lavender (EDTA): ethylenediaminetetraacetic acid anticoagulant. Chelates calcium to prevent clotting. Produces whole blood or EDTA plasma. Used for full blood count, blood film, HbA1c, ESR, blood group and screen, and most haematology requests. Requires 8 to 10 inversions after filling.
- Light blue (sodium citrate): coagulation tube. Fixed 1:9 citrate-to-blood anticoagulant ratio. Must be filled to exactly the correct volume. Used for PT, APTT, fibrinogen, D-dimer, and all coagulation studies. Requires 3 to 4 inversions. Critically sensitive to underfilling.
- Green (lithium heparin): heparin anticoagulant with or without gel. Produces plasma rapidly without waiting for clotting. Used for urgent biochemistry, plasma potassium, and tests requiring plasma rather than serum. Requires 8 to 10 inversions. Not suitable for haematology or coagulation testing.
- Grey (fluoride oxalate): glucose preservation. Sodium fluoride inhibits glycolysis; potassium oxalate anticoagulates. Prevents in vitro glucose consumption after collection, stabilising glucose levels for up to 24 hours at room temperature. Used for fasting glucose, glucose tolerance tests, and lactate. Requires 8 to 10 inversions.
- Black (sodium citrate 3.2% or 3.8%): ESR tube. Specific citrate concentration for Westergren ESR method. The tube volume and fill ratio are specifically designed for this application. Not interchangeable with the light blue coagulation citrate tube.
- Pink or tan (EDTA for blood bank): blood bank EDTA. Same additive as standard EDTA but specifically labelled and tracked for blood bank applications including crossmatch and group and screen. Must bear the patient identifier applied at the bedside.
- Dark blue (trace element): metal-free tube. Manufactured without metal contamination for trace element analysis including zinc, copper, lead, and manganese. Standard tubes contain trace metal contamination sufficient to interfere with these assays.
Practical application
Using the colour reference in daily collection practice
Always read the label as well as the colour
Tube cap colour is a rapid identification aid, not a substitute for reading the label. Minor colour variations exist between manufacturers, and some specialist tubes share a colour with a more common tube while containing a different additive. Always confirm the additive and volume on the tube label before use, particularly when working with tubes from an unfamiliar supplier or when a colour does not match your expectations.
Colour coding in the order of draw
Tube colours guide the order of draw sequence. The standard UK order is: blood culture bottles, then plain red or yellow SST, then light blue citrate, then green heparin, then purple EDTA, then grey fluoride oxalate. When in doubt about the order, refer to your laboratory's current SOP, as recommendations can vary slightly between institutions based on local evidence.
Paediatric and specialist tubes
Paediatric blood collection tubes are available in all the standard additive types at smaller volumes, typically 1 to 2 ml, with the same colour coding as adult tubes. Specialist tubes including RNA stabilisation tubes, cell-free DNA tubes, and others may use colours outside the standard clinical range. These specialist tubes will be clearly labelled with their specific application.
All tube colours in stock
Blood collection tubes in all standard additive types
Charles Medical supplies blood collection tubes in all standard cap colours and volumes. Next-day UK delivery.
For the order in which coloured tubes should be drawn, see The Correct Order of Draw in Blood Collection.
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Back to the Blood Collection Tubes Knowledge Hub
This article is part of our complete blood collection tube knowledge base, covering tube types, colours, additives, order of draw, pre-analytical errors, disposal, and everything phlebotomists and laboratory staff need to know.
Keep reading
Related guides in this hub
The Correct Order of Draw in Blood Collection applies the colour reference to the sequencing decision. Why the Right Tube Matters for Each Blood Test explains what happens when the wrong colour tube is used. And Differences Between Serum and Plasma Tubes Explained clarifies the distinction between gold SST and green heparin tubes for biochemistry.
Frequently asked
Tube colour questions answered
What colour tube is used for a full blood count?
Purple or lavender EDTA tube. This is the standard tube for all haematology requests including FBC, blood film, reticulocytes, and ESR using the EDTA method. Invert 8 to 10 times immediately after filling.
What colour tube is used for coagulation tests?
Light blue sodium citrate tube. This tube must be filled to exactly the correct volume because the 1:9 citrate-to-blood ratio is critical for accurate coagulation results. Even moderate underfilling produces falsely abnormal results.
What is the difference between a gold SST and a plain red tube?
Both produce serum. The gold SST contains a clot activator that speeds clotting and an inert gel that separates serum from the clot during centrifugation. The plain red tube has no additive and no gel; blood clots naturally and the serum must be separated manually. The SST is more widely used in routine practice; the plain red tube is used where gel may interfere with specific assays.
What colour tube is used for blood glucose?
Grey fluoride oxalate tube. The sodium fluoride inhibits glycolysis and stabilises glucose for up to 24 hours at room temperature, which is necessary for accurate glucose measurement. Using a plain or SST tube for glucose allows in vitro glucose consumption, which falsely lowers the result.